1. Field of Invention
This invention relates to a detecting head assembly capable of simultaneously detecting radioactive emissions (such as beta particles) from a multiplicity of samples. The detecting head assembly may be used in apparatus for counting ionizing events due to beta particles emitted by a radiochromatogram or an electrophoretogram (hereinafter called "radiograms"), or by biological or other samples.
2. Status of Prior Art
A detecting head assembly is already known from EP-A-0112645 which comprises electrode sub-assemblies including a grid of cathode strips which cross over an array of anode wires to form a plurality of detector crossing points. The crossing points detect individual ionizing events due to the ionization of a gas or mixture of gases by beta particles emitted from radioactive materials in a radiogram. In order to improve spatial resolution, a mask having a plurality of radiation transmissive zones or apertures (corresponding in position and number with the anode/cathode crossing points) is supported between a sample holder and the electrode sub-assemblies. The detecting electrode sub-assemblies and the mask are mounted in scanning means which are slidably supported in juxtaposition to the sample holder. The detecting electrode sub-assemblies (crossing points) can thereby be scanned across a sample. In a preferred arrangement, respective `x` and `y` coordinate stepper motors are used to provide a raster scan of a plurality of regions or frames in the sample zone. The output signals from the detecting electrode assemblies are supplied to either conventional pulse counting means, or they are coded (with respect to the position coordinates of individual ionization events) and the coded signals are then supplied to a computer where they are processed in order to derive information relating to the distribution of radioactivity in the sample.
The apparatus described in EP-A-112645 is particularly useful in providing a high resolution "picture" of the spatial distribution of radioactivity in a radiogram and it was primarily developed for visualising the distribution of radioactivity in a sample. There is, however, a need for an efficient, multiple sample, radioactivity detector of relatively straightforward and robust construction which can be used, for example, in the field of medical diagnostics and biomedical research, to count beta particle emissions from radioactive materials taken from radiograms or in biological or other samples where only the radioactivity of the samples is required and not the distribution of radioactivity within a sample. The present invention seeks to solve this problem.